Who is the oath of office administrated by?

Answer 1

In the absence of more details, I presume that the question means to ask: "In the United States federal government, who administers the oath of office of the president?"

Traditionally, the chief justice of the United States Supreme Court administers the oath of office of the president. See http://memory.loc.gov/ammem/pihtml/pioaths.html This is traditional only, and is not mandated by the constitution nor is it codified in U.S. law. The administrator is intended to be someone of legal authority, such as a judge or justice of the Supreme Court.

What's interesting is that the oath (or affirmation) is actually quoted in the Constitution (Article II, Section 1). The 35 word quote is the only quote in the Constitution.